502 



THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



indicated by increasing application of the prin- 

 ciple of measurement, and by the importance 

 which is attached to numerical results. And this 

 very necessary condition for progress may, I 

 think, be fairly described as one of the main 

 features of scientific advance in the present day. 



If it were my purpose, by descending into the 

 arena of special sciences, to show how the most 

 various investigations alike tend to issue in meas- 

 urement, and to that extent to assume a mathe- 

 matical phase, I should be embarrassed by the 

 abundance of instances which might be adduced. 

 I will therefore confine myself to a passing no- 

 tice of a very few, selecting those which exemplify 

 not only the general tendency, but also the special 

 character of the measurements now particularly 

 required, viz., that of minuteness, and the indi- 

 rect method by which alone we can at present 

 hope to approach them. An object having a di- 

 ameter of an 80,000th of an inch is perhaps the 

 smallest of which the microscope could give any 

 well-defined representation ; and it is improbable 

 that one of 120,000th of an inch could be singly 

 discerned with the highest powers at our com- 

 mand. 1 But the solar beams and the electric 

 light reveal to us the presence of bodies far 

 smaller than these. And, in the absence of any 

 means of observing them singly, Prof. Tyndall 

 has suggested a scale of these minute objects in 

 terms of the lengths of luminiferous waves. To 

 this he was led, not by any attempt of individual 

 measurement, but by taking account of them in 

 the aggregate, and observing the tints which they 

 scatter laterally when clustered in the form of 

 actinic clouds. 2 The small bodies with which ex- 

 perimental science has recently come into con- 

 tact are not confined to gaseous molecules, but 

 compi-ise also complete organisms ; and the same 

 philosopher has made a profound study of the 

 momentous influence exerted by these minute or- 

 ganisms in the economy of life. 3 And if, in view 

 of their specific effects, whether deleterious or 

 other, on human life, any qualitative classifica- 

 tion or quantitative estimate be ever possible, it 

 seems that it must be effected by some such 

 method as that indicated above. 



Again, to enumerate a few more instances of 

 the measurement of minute quantities, there are 

 the average distances of molecules from one 

 another in various gases and at various press- 



1 See Sorby's "Address to the Microscopical So- 

 ciety," 1876. 



2 " Philosophical Transactions of the Royal Soci- 

 ety," 1870, p. 333 ; and 1876, p. 27. 



3 •' Philosophical Transactions," 1877, p. 149. 



ures ; the length of their free path, or range, 

 open for their motion without coming into colli- 

 sion ; there are movements causing the pressures 

 and differences of pressure under which Mr. 

 Crookes's radiometers execute their wonderful 

 revolutions. 1 There are the excursions of the air 

 while transmitting notes of high pitch, which, 

 through the researches of Lord Rayleigh, appear 

 to be of a diminutiveness altogether unexpected. 5 

 There are the molecular actions brought into play 

 in the remarkable experiments by Dr. Ker, 3 who 

 has succeeded, where even Faraday failed, in 

 effecting a visible rotation of the plane of polari- 

 zation of light in its passage through electrified 

 dielectrics, and on its reflection at the surface of 

 a magnet. To take one more instance, which 

 must be present to the minds of us all, there are 

 the infinitesimal ripples of the vibrating plate 

 in Mr. Graham Bell's most marvelous invention. 

 Of the nodes and ventral segments in the plate 

 of the telephone which actually converts sound 

 into electricity and electricity into sound, we can 

 at present form no conception. All that can now 

 be said is that the most perfect specimens of 

 Chladni's sand-figures on a vibrating plate, or of 

 Kundt's lyeopodium heaps in a musical tube, 4 or 

 even Mr. Sedley Taylor's more delicate vortices 

 in the films of the phoneidoscope, 5 are rough and 

 sketchy compared with these. For, notwith- 

 standing the fact that in the movements of the 

 telephone-plate we have actually in our hand the 

 solution of that old world-problem, the construc- 

 tion of a speaking-machine, yet the characters in 

 which that solution is expressed are too small for 

 our powers of decipherment. In movements such 

 as these we seem to lose sight of the distinction, 

 or perhaps we have unconsciously passed the 

 boundary between massive and molecular mo- 

 tion. 6 



Through the phonograph 7 we have not only 

 a transformation, but a permanent and tangible 

 record of the mechanism of speech. But the 

 differences upon which articulation (apart from 

 loudness, pitch, and quality) depends, appear, 

 from the experiments of Fleeming Jenkin and of 



1 " On Attraction and Repulsion resulting from 

 Radiation," "Philosophical Transactions," 1874, p. 

 501 ; 1875, p. 519 ; 1876, p. 325. 



2 Thilosophical Magazine, April, 1878. 



« Ibid., 1875, vol. ii., pp. 337, 446; 1877, vol. i., p. 

 321 ; 1878, vol. i., p. 161. 



4 Poggendorff's Annalen, torn, xxxv., p. 337. 



5 Royal Society's " Proceedings," 1878. 



6 The papers on the telephone are too numerous to 

 specify. 



T See Various papers in Nature, and elsewhere, dur- 

 ing the last twelve months. 



